1. Field of the Invention
This invention relates to an X-ray diagnostic apparatus sing an X-ray flat panel detector and a method for controlling the same X-ray diagnostic apparatus.
2. Description of the Prior Art
In a field of X-ray image diagnosis, instead of radiography with conventional X-ray film, an image intensifier (I.I)-TV system has been widely used. The I.I-TV system has such advantages that X-ray image diagnosis can be performed immediately without a wait time for development unlike the silver salt film, real-time fluoroscopy as well as radiography can be carried out, and management, storage, transporting and copying of an image are facilitated by converting an image to digital data by video capture.
FIGS. 1A, 1B show a conventional X-ray diagnostic apparatus utilizing such an I.I-TV system.
In this X-ray diagnostic apparatus, X-ray is projected from an X-ray source 100 to a patient and an an X-ray image passing through the patient is intensified by I.I 101 and converted to an optical image. This optical image is taken by a TV camera 103 via an optical system 102 and subjected to a predetermined image processing by an image processing portion 104 and then supplied to a monitor device 105. As a result, the X-ray image can be observed via the monitor device 105.
In this X-ray diagnostic apparatus, magnification for the X-ray image is variable inside the I.I 101. If an entire X-ray image irradiated to an input surface of the I.I 101 is required to be observed, this entire X-ray image is focused on an output surface of the I.I 101 as an optical image by controlling an electronic lens provided inside the I.I 101. If part of the X-ray image irradiated to the input surface of the I.I 101 is required to be observed, this part of the X-ray image is focused on the output surface of the I.I 101 as an optical image by controlling the electronic lens as shown in FIG. 1B.
The X-ray diagnostic apparatus provided with the I.I 101 is capable of changing the magnification for the X-ray image by the electronic lens. Further, by narrowing an observation region for the X-ray image irradiated to the input surface of the I.I, a high resolution optical image can be obtained easily.
The size of the imaging region of the I.I-TV system is determined by a bore of the an I.I. Recently, I.I having a bore as large as 16" has been produced to meet a demand for enlargement of an imaging region. However, if the bore of the I.I is increased, a depth of its detecting system as well as the imaging region is increased, so that its weight also naturally increases. As a result, such an X-ray diagnostic apparatus becomes difficult to use. Further, the service life of the X-ray diagnostic apparatus is short because of tube structure.
Thus, an X-ray diagnostic apparatus utilizing a thin type X-ray flat panel detector has been regarded as a hopeful alternative to compensate for such disadvantages of the I.I-TV system.
The X-ray flat panel detector is capable of reading an X-ray strength distribution projected on a plane as data in each pixel. This X-ray flat panel detector is classified to two types. One is an indirect type in which the X-ray is converted to a light wavelength which can be detected by an photoelectric conversion element by using a fluorescent material, and the other one is a direct type in which the X-ray is directly detected by a semiconductor such as selenium. Both types of the X-ray flat panel detectors are produced by applying fine processing technology like semiconductor production technology, liquid crystal display panel production technology or the like and a panel of about 40 cm.times.40 cm can be produced now.
Recently, a case using the X-ray radiography to grasp a patient's condition has been increased in an emergency field such as an accident or disaster. In the conventional X-ray diagnostic apparatus, because its radiography region is relatively small, positioning for taking a region of interest within that radiography region must be achieved in even an emergency case or a number of radiographs must be taken to radiograph an entire field of the region of interest.
However, in case of the conventional X-ray diagnostic apparatus, if its X-ray source and X-ray detector are connected to each other in the system, detection of the position thereof and control of the position thereof must be carried out so as to place the X-ray detector at a position on which the X-ray is irradiated, so that labor and time are needed for this positioning.
Further in the conventional X-ray diagnostic apparatus, if the X-ray source and X-ray detector are not connected in the system, the position thereof must be determined by a number of pre-irradiation to place the detector at a position on which the X-ray is irradiated. Thus, in addition to the above problem, there is another problem that exposure to the X-ray is increased.
Further in a case of an X-ray diagnostic apparatus utilizing a large vision field X-ray flat panel detector, because entire pixel data of that X-ray detector are collected, it takes a long time to collect the data, and further it takes time and labor to extract and display data including an interest position from the collected data. That is, there is still another problem that high speed and detailed radiography is impossible.
From another point of view, the X-ray diagnostic apparatus is demanded to satisfy the following two points. One of them is ability to observe a wide region at a relatively low spatial resolution. The other is the ability to observe at a relatively high spatial resolution although the area is small. To satisfy these two requirements, an X-ray diagnostic flat panel detector having as high a spatial resolution as possible and as wide a vision field as possible is demanded to be produced.
However, if such an X-ray flat panel detector having the high spatial resolution and large vision field is used, data amount per frame output from the X-ray flat panel detector increases tremendously, thereby producing an inconvenience that its image processing circuit at a next step is burdened with a large load. Particularly, in case where X-ray consecutive image data (e.g., 30 frames/second) is collected, data transmission and processing at a very high data rate must be carried out, so that an expensive unit needs to be provided as a signal transmission system and signal processing system.
In a field of X-ray image diagnosis, angiography has been important for diagnosis on a circulatory organ such as the heart and blood vessel. According to this angiography, a tube called a catheter is inserted into a blood vessel up to near an object artery of a patient under fluoroscopy and then X-ray contrast medium is injected into the blood vessel through the catheter. The X-ray contrast medium flowing in the blood vessel is radiographed at a high speed with the X-ray diagnostic apparatus. As a result, the condition of the blood in the blood vessel is visualized.
Particularly, this inspection is carried out for diseases of the circulatory organ like myocardial infarction, cerebral infarction. Because the tube is inserted into the blood vessel, this inspection is conducted in a relatively clean inspection room. In this case, a patient lies on a diagnostic bed for the catheter and an operator and several assistants stand around him. A pair or two pairs of the X-ray sources and X-ray TV units (hereinafter referred to as X-ray TV chain) for obtaining X-ray images are placed just beside the patient (see FIG. 2).
In such an environment, a supporting device supporting the X-ray tube and X-ray TV unit is brought near to the patient as required from various angles like the head portion, leg, right hand side, left hand side to ensure a better access to the patient (see FIG. 3)
Conventionally, when the I.I.-TV camera is used as the X-ray TV system, even if the direction for approaching the I.I to the patient is changed, the X-ray image is obtained with a constant direction by turning the image by, for example, image processing because the image formed by the I.I.-TV system is circular.
However, in a case where the X-ray flat panel detector is used in the X-ray diagnostic apparatus, if the insertion direction of the supporting device to the patient is changed, the X-ray flat panel detector fixed on the supporting device is disposed in a different direction depending on the insertion direction relative to the patient.
Thus, if the X-ray detecting device is of rectangular shape, its corner moves relative to the patient corresponding to the direction of the supporting device. As a result, there occurs a problem that the patient feels a fear that that corner may strike him.
Further, in a case of radiographing the same portion, the direction of an image displayed on the monitor changes depending on a direction in which the X-ray--TV chain is brought to the patient.
Meanwhile, in conventional cardiac catheter inspection, generally, fluoroscopy by a bi-plane inspection unit is carried out because a complicated blood vessel system needs to be traced spatially.
In this bi-plane inspection unit, a C-arm holding device which is a floor placed type X-ray diagnostic apparatus (F: frontal holding device) and a .OMEGA.-arm holding device which is a mounting type (ceiling hoisting type) X-ray diagnostic apparatus (L: lateral holding device) are used at the same time and then fluoroscopy is achieved by irradiating a small mount of the X-ray continuously from each holding device to obtain an X-ray consecutive image. Consequently, fluoroscopy images of two directions are obtained at the same time.
FIG. 4 shows a schematic view on operation of the bi-planes in the conventional angiography and FIG. 5 shows fluoroscopy images of the frontal holding device and lateral holding device obtained by this bi-planes operation.
As for positioning for this angiography, the C-arm 201 of the frontal holding device (F) is set to RAO 30.degree. and the .OMEGA.-arm 200 of the lateral holding device (L) is set to LAO 600.
Although a necessary vision field for the cardiac catheter inspection is 9 inch, intimate fluoroscopy at an enlargement mode of 6 inch is carried out by a vision field changing function of an image intensifier (I.I.). because a high quality X-ray image which enables to see blood vessel stricture or a tip of a fine catheter is demanded.
Because an entire cardiac blood vessel cannot be taken into a 6-inch vision field in the cardiac angiography using the frontal holding device (F) and lateral holding device (L), a table panel 202 on which a patient lies and two holding devices including the frontal (F) 201 and lateral (L) 200 are operated to trace a flow of contrast medium. Although FIG. 5 shows both the 9-inch vision field and 6-inch vision field, a fluoroscopy image which is actually displayed on the monitor is the 6-inch vision field fluoroscopy image.
In an operating procedure following a flow of the contrast medium in the vision field for fluoroscopy, the table panel 202 on which the patient lies is slid in the direction (to the right) indicated by the arrow A in FIG. 4 and the .OMEGA.-arm 200 of the lateral holding device (L) is moved in the direction (upward) indicated by the arrow B in the same figure. As a result, as shown in FIG. 5, the fluoroscopy image of the frontal holding device (F) is displayed such that an image in the center of the screen is slid to the left and the fluoroscopy image of the lateral holding device (L) is displayed such that an image in the center of the screen is slid to the right.
Next, the table panel 202 is slid in the direction (head direction) indicated by the arrow C of FIG. 4. Consequently, as shown in FIG. 5, as a fluoroscopy image of the frontal holding device (F), an end portion of the blood vessel which was out of the vision field is displayed by sliding the table panel 202. Then, as a fluoroscopy image of the lateral holding device (L), an end portion of the blood vessel which was out of the vision field is also displayed.
Each fluoroscopy image (DSA image) displayed on the monitor by such an operation is observed at real time to trace a flow of the contrast medium in the cardiac blood vessel.
However, in such a cardiac angiography, the table panel on which the patient lies and the two holding devices including the frontal holding device and lateral holding device must be operated to trace a flow of the contrast medium in the blood vessel. This operation is very complicated and requires a skill. Thus, it is very hard for a single operator to operate the frontal holding device and lateral holding device in two directions in a combined manner. Therefore, conventionally, there exists a problem that specialized operators (totally two operators) are required to operate the frontal holding device and lateral holding device.